The invention relates to a method and arrangement for predicting perioperative myocardial ischemia.
Patients with myocardial ischemia after non-vascular and non-cardiac vascular surgery have 3 to 9-fold risk of adverse cardiac events, respectively, and cardiac complications account for more than half of the deaths. Especially prolonged ischemia over 10 minutes has been recently shown to be a strong predictor for postoperative death and myocardial infarction. The prevalence of perioperative myocardial Ischemia in unselected hip fracture patients has been reported to be over 30%. The term perioperative refers to time before the operation, under the operation and after the operation. Complications are mainly due to ischemic events, pneumonia and lung embolism. The 3-year mortality rate is over 30%, and almost half of those who survive are permanently institutionalized.
The autonomic nervous system plays a significant role in the pathophysiology of perioperative ischemia. There is evidence that sympathetic activation has an important role in the onset of adverse cardiac events. Adrenergic activity and plasma catecholamine levels change considerably in the postoperative period, which may predispose to myocardial ischemia by altering relationship between myocardial oxygen demand and supply. Furthermore, increased sympathetic activation during REM sleep has been suggested to be associated with the circadian pattern of ischemia occurring most frequently during early morning hours.
Heart rate variability (HRV) measures from ambulatory electrocardiograph recordings are widely used in the assessment of cardiovascular autonomic regulation. Recent studies suggest that newer measures of HRV, such as fractal analysis methods can complement the traditional time and frequency domain HRV measures in risk stratification of patients with heart disease. These new dynamic analysis methods describe qualitative rather than quantitative properties of HRV. Fractal correlation properties exhibit long-range correlations between RR-intervals; i.e., interbeat interval at every time point is partially dependent on the intervals at all previous time points. An article “Fractal dynamics in physiology: Alterations with disease and aging” Goldberger et al, Feb. 19, 2002, can be mentioned as an example of the prior art.
The American Heart Association has issued guidelines to identify patients at greater risk for postoperative adverse cardiac outcome preoperatively but diagnostic tools with better performance in risk stratification are still needed.